The Shake-Out on Sediment

(Originally published October 2003)

Hanes usually starts off with some cheesy introduction like "It's sedimentary, my dear Watson." OK, he just did. Last year Hanes discussed the in's and out's of decanters and decanting wines. Yet, he did not go into detail about one of the primary reasons to decant, the sediment. Never assuming his kind, doe-eyed readers know of these things, we must now ask the questions: what is sediment and why does it occur?

Our quick initial answer is that sediment is the deposit of solid matter that settles into the bottom of a bottle of red wine, particularly an older bottle. It occurs naturally due to certain chemical processes. Sediment tastes bitter and astringent and should never be poured into a glass.

The presence or absence of sediment depends on many factors, driven primarily by a multitude of winemaking decisions and methods. During the fermentation process dead yeast cells, grape seeds, stems, skins and pulp settle at the bottom of the fermentation container (be it oak barrel, stainless steel or glass vat, etc.). This sediment is called the "lees." Lots of important flavors and/or chemical properties reside in the lees so sometimes the decision will be made to stir them up from the bottom to come into contact with the juice above. This process is called "bâtonnage." Sometimes this stirring helps the process of malolactic conversion of malic acid to lactic acid, making the wine's texture softer and creamier. This is because bacteria is required to trigger the conversion and these bacteria exist in the lees. While this process is more prevalent with white wines, it does occur with many red wines as well.

While many wines gain complexity from extended contact with the lees (for example, Muscadet wines from France's Loire Valley often go so far as to label their wines as "sur lie," or "on the lees"), a winemaker has to decide how long to allow the sediment to remain in contact with the wine. The first process employed to remove sediment is called "racking." What happens is that the wine is slowly poured from one container to another until all that remains in the first container is sediment, which is then discarded. A given wine may be racked multiple times during the maturation process to remove newly formed sediment.

After these basic decisions are made, further tough choices must be made. Some winemakers make extra efforts to ensure there is no cloudiness in the finished wine. The process they then employ is called "fining." Fining agents such as egg whites, gelatine, bentonite, etc. are added to the wine and they bind with the tiny bits of sediment that is causing the cloudiness. The resulting substance (called colloids) are heavy enough then to fall to the bottom of the container, thus clearing up the wine. There's lots of reasons a winemaker chooses one or another fining agent but that shit's boring. What's important is that the sediment forms at the bottom of the container and can then be racked off.

There are other winemaking decisions still to be made in the ongoing bloody battle against sediment! The first to mention is cold stabilization. White wines don't throw much sediment in the bottle but a deposit called tartrates can form. These crystal-like materials usually attach to the cork but they can also accumulate in the bottom of the bottle. They are entirely harmless (being odorless and tasteless) but they represent an aesthetic flaw. And they're kind of crunchy. Cold stabilization is a process whereby the wine is subjected to very low temperatures before bottling, making the wine resistant to tartrate formation or causing any potential tartrates to form so they can be removed prior to bottling. Cold stabilization does also help many red wines avoid later tartrate formation but on the whole it's more about the whites (note that non-cold stabilized reds that are stored for long periods in a refrigerator may develop tartrates or sediment).

Another winemaking technique is filtering. The wine is passed through a filter fine and small enough to remove sediment and other substances deemed superfluous to the desired finished wine. There are many methods of filtration (sheet, membrane, sterile, etc.) but they all more or less end up doing the same thing  removing sediment.

Once in the bottle, many chemical processes continue to change the wine over time. With finer, more pedigreed wines meant to be aged these processes play out over a period of many years. It's rare to find sediment in wine meant to be consumed within the first 2-3 years after bottling. These wines have been sufficiently racked, fined and/or filtered to make sure there's no glop in your Merlot. It's important to note in passing that even if no sediment forms (indicating a wine that has aged some or not been subjected to a lot of racking and/or fining), wines do change in character over as little a period of time as a 4-6 months. Thus, the bottle of Sancerre you drank in January may taste quite different by June. There's a lot going on that's much less visible than sediment formation.

With wines that are deliberately aged you can expect to find some tartrate crystals, which is the crystallization of potassium bitartrate. With red wines you are more likely to encounter tannins (or other compounds which go by exciting names such as anthocyanins) that have been turned into sediment through phenolic polymerization, whereby the compounds become too heavy to remain suspended in the wine. This explains why a ruby or purple wine when young turns into a brown, red brick or orange wine when aged. Additionally, phenolics and tannin polymers change over time so that in addition to changes in color, there are changes in mouth feel. So, it's quite plausible that the sediment in your bottle of aged Bordeaux is the result of the softening of the wine's tannins over time. It's not necessarily that "resolved tannins" (i.e., tamer, less drying or puckering tannins) must create sediment but there's some loose correlation. It's good to mention that there is nothing toxic nor inedible about sediment. It's a textural and aesthetic thing, not a potential health hazard.

It's paramount to underscore that the presence of sediment is not necessarily a sign of a flawed nor bad wine. Hell, in many instances it is a sign of the direct opposite, that the wine was not unfortunately stripped of potential additional flavor and color via the fining and filtering out of the elements which eventually would have become sediment. Even if the wine is relatively young, sediment may be evidence that the winemaker favors a more "natural" approach to winemaking, ready to allow it to develop its inherent complexity without too much direction from a human hand. Hanes is no dyed-in-the-wool romantic when it comes to these sort of issues but he does have plenty of firsthand evidence which suggests that wines with sediment do often possess an intensity of flavor that does not feel processed or intentionally directed.

The lesson is this. If a salesperson or sommelier extols a wine's clarity as a sign of its superior virtue, take everything s/he says with a grain of salt -- chances are you can see through her/his head as easily as the wine they are recommending.